HYBRID WALNUTS FOR FORESTRY PRODUCTION

Specific care of the walnut:

· Land preparation before planting:

1) carrying out a good crossed subsoiling and removing the root rests is critical for the subsequent health of the plantation,

2) improving the structure with an organic matter supply is recommended as well as balancing the soil content in mineral elements with an adequate basal dressing.

· Water supply:

1) A good watering of the plantation is essential,

2) as well as the water supply during the vegetative period in the great part of the potential Spanish planting zones (more than 700 mm of annual rain is required). Trees must not suffer from water stress to grow regularly.

Proper crop places can be agricultural fields with fresh and deep lands, meadows, prairies or agricultural field edges among others.

 

Plant material:

The best adapted materials to these production conditions seem to be so far the hybrids between Juglans species. Several world walnut species have shown their capacity to cross with each other naturally. The resulting hybrid material, known as Juglans intermedia, is characterized by a great vigour - the hybrid vigour - and a very low or even no fruit production capacity. This behaviour that openly favors the vegetative development implies a valuable advantage for the forestry production.

Among these hybrids, those which can be found in the market are controlled seed seedlings of Black walnut x Common walnut, and specially Ng23 x Ra and Mj209 x Ra. Both hybrids are produced in production fields with controlled seed in France. Both Ng23xRa and Mj209xRa materials have shown a high suitability for the forestry production, although the descendant homogeneity, their quality, directly depends on the thorough selection carried out in the production nursery (there is always a percentage of non hybrid individuals to be deleted).

Due to the characteristic vigour of these materials it is recommended to plant with a 6 m x 6 m spacing, that is 278 trees per hectare. If plantings are done with a narrower spacing, several tree thinning operations should be carried out.

Tree training:

In this kind of forest exploitation training pruning is essential. Trees must get their definitive stem during the 6-7 first planting years.

Operations should be carried out in wintertime to remove the bad located lignified branches, in springtime if dominance has to be recovered after late frost damages, and in summertime when bud growth rate slows down to remove competitions that hinder the axis to maintain its natural hegemony. After the third year it is recommended to maintain the balance between 1/3 of trunk and 2/3 of height top and to sistematically remove branches with diameters above 3-4 cm.

Growths should be always carefully controlled to avoid imbalances, particularly in windy zones where the use of stakes could be essential.

Shortage of leafy species woods has lead to think about a more intensive production of these species and about forest plantings. The use of agricultural fields with this aim is relatively recent, France and Italy being pioneering countries. Walnut trees (Juglans sp.) were one of the selected species for this type of exploitations, some of them already in felling phase. The first walnut plantations in Spain with this objective date from 1994.

In this type of forest plantations a shortening of the production shift is expected though without neglecting the quality of the wood obtained by such noble species like walnut tree. Prices of walnut wood range widely between 600€/m3 and 1500€/m3 depending on stem quality.

In an intensive-type walnut exploitation, production objectives are:

1) a minimum stem of 3.5 m, flaws-free,

2) a diameter at 1.30 m (dbh) higher than 45 cm,

3) a regular ring growth,

4) and an approximate age of 25 years so that wood reaches its maturity.

These requirements will be only obtained with:

1) the use of adequate plant material,

2) the use of proper tree training techniques (during the first 5-6 years),

3) and avoiding water or phytosanitary stress situations.

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